1. Field of the Invention
The present invention relates generally to so-called horizontal bandsaw machines in which an endless bandsaw blade is trained between wheels so as to perform cutting operations and, more particularly, to an apparatus for tensioning a bandsaw blade in horizontal bandsaw machines.
2. Description of the Prior Art
Horizontal bandsaw machines comprise a base having a work-table on which workpieces or materials to be cut are placed and a saw head assembly which encloses or holds a flexible endless bandsaw blade and is so arranged as to be raised away from and lowered towards the work-table. In the saw head assembly, the flexible endless bandsaw blade is trained around bandsaw wheels or pulleys which are mounted for rotation on spaced substantially parallel axes so as to perform cutting operations. One of the bandsaw wheels is power driven and acts as a driving wheel to drive the bandsaw blade, and the other bandsaw wheel which is referred to as driven wheel is drawn or biased together with its shaft in a radial direction away from the driving wheel to tension the bandsaw blade. Also, the bandsaw blade trained around the driving and driven wheels is slidably guided by a plurality of guide means so that its cutting edge, when passing through the cutting zone where cutting is performed, may be kept perpendicular to the work-table. Thus, in cutting operations, the saw head assembly with the bandsaw blade driven therein is lowered from its raised position towards the work-table so that the bandsaw blade may cut into the workpieces placed on the work-table.
In the horizontal bandsaw machines of the above described arrangement, it is necessary to keep the bandsaw blade always adequately tensioned between the driving and driven wheels so as to prevent the bandsaw blade from being uselessly worn and broken and perform accurate cutting operations. The lack of the tension of the bandsaw blade will reduce the friction between the bandsaw blade and the driving and driven wheels with a result that the driving wheel will slide on the bandsaw blade without driving the same or otherwise the bandsaw blade will slip off from the driving and driven wheels. Also, if the driving wheel slides on the bandsaw blade, they are worn by each other because of friction, and besides the bandsaw blade will be broken, since it will be forcedly fed into a workpiece to be cut by the saw head assembly while not driven by the driving wheel. Furthermore, as is readily understood by those skilled in the art, the bandsaw blade, while not adequately tensioned, will be unable to perform accurate cutting, even if it is driven by the driven wheel. Since the bandsaw blade will gradually elongate between the driving and driven wheels as it continues performing operations, it is necessary to additionally tension the bandsaw blade to keep the same always adequately tensioned.
On the other hand, when the bandsaw blade is to be firstly installed, initially the driven wheel is slightly moved towards the driving wheel and then the bandsaw blade is installed around the driving and driven wheels and lastly the driven wheel is drawn away from the driving wheel to tension the bandsaw blade. In this procedure, the bandsaw blade is held by hand around the driving and driven wheels when tensioned so that it will not drop off from the driving and driven wheels.
In the past, various attempts have been made to tension the bandsaw blade and keep the same always adequately tensioned in horizontal bandsaw machines, but all of the prior art apparatus for such purposes have suffered from serious shortcomings. In conventional apparatus, for example, a lead screw has been so arranged as to be manually operated to tension the bandsaw blade, and a spring means has been employed so as to compensate for lack of the tension of the bandsaw blade, but of course the bandsaw blade cannot be adequately and accurately tensioned in such manually operated apparatus. Also, although there have been more improved apparatus in which the bandsaw blade is hydraulically tensioned, such apparatus have been divergent and complicated in construction and have not been easy to operate. Among others, the most serious disadvantage with conventional apparatus for tensioning the bandsaw blade in horizontal bandsaw blade has been the fact that more than one operator is required to first install the bandsaw blade and tension the same between the driving and driven wheels. More particularly, when the bandsaw blade is to be first installed, not only an operator has been necessary to tension the bandsaw blade, but also at least one other operator has had to hold the bandsaw blade around the driving and driven wheels to prevent the same from dropping off therefrom.